Data from: Endocranial anatomy of a new fossil porpoise (Odontoceti: Phocoenidae) from the Pliocene San Diego Formation of California

The Pliocene fossil porpoise SDSNH 65276 has extremely elongate mandibular morphology, unlike that of any marine amniote, and is superficially most similar to the living bird species known as skimmers (Rynchops sp.). Endocasts of the pterygoid sinuses and endocranial cavity were digitally segmented from high-resolution X-ray CT scans of the specimen to explore internal anatomy of functionally and phylogenetically important anatomical features of this specimen and odontocetes in general. The sinuses are similar in volume and shape to extant porpoise species, but the dorsal extension of the preorbital lobes are particularly elongate as in the harbor porpoise (Phocoena phocoena). The cranial endocast also shows similarities with extant porpoises, but has much deeper interhemispheric fissures, which are filled by ossified meninges, particularly a deep falx cerebri and shallower tentorium cerebelli. Ossifications of these parts of the meninges may reflect faster angular accelerations of the head, deeper diving ability, or both. Penetrations of the endocranial cavity for cranial nerves and blood vessels are like those of extant porpoises. The internal skull morphology of this unique delphinoid sheds additional light both on its phylogenetic affinities and novel odontocete adaptations.

上新世（Pliocene）化石鼠海豚标本SDSNH 65276具有极为延长的下颌形态，与所有已知海生羊膜动物均存在显著差异，外观上与现生的剪嘴鸥属（Rynchops sp.）鸟类最为相似。研究人员通过对该标本开展高分辨率X射线计算机断层扫描（CT），对其翼窦（pterygoid sinuses）与颅腔（endocranial cavity）的内腔模进行了数字化分割，以探究该标本以及广义齿鲸类（odontocetes）中兼具功能与系统发育重要性的解剖特征的内部构造。该翼窦的体积与形态与现生鼠海豚物种相近，但眶前叶的背侧延伸部分尤为修长，与港湾鼠海豚（Phocoena phocoena）的特征一致。该颅内腔模同样与现生鼠海豚存在相似之处，但其大脑半球间裂更深，该裂隙由骨化脑膜填充，其中以较深的大脑镰（falx cerebri）与较浅的小脑幕（tentorium cerebelli）最为典型。上述脑膜区域的骨化现象，可能反映了头部更快的角加速度、更强的深潜能力，或二者兼具。颅腔中供脑神经与血管穿行的孔道结构与现生鼠海豚一致。这一独特的海豚总科物种的颅骨内部形态，为其系统发育亲缘关系以及全新的齿鲸适应性特征研究提供了新的见解。